Abstract
Secondary Ion Mass Spectrometry (SIMS) has been widely used in the semiconductor field, because it enables highly sensitive imaging of element distribution and depth analysis. The SIMS using MeV-energy heavy ion (MeV-SIMS) opened new possibilities for investigating chemical composition, structure as well as for imaging, which are very important for organic and biological materials. We have demonstrated molecular imaging of a rat brain with the MeV-SIMS technique. Furthermore, we have developed an atmospheric pressure SIMS technique that uses a MeV-energy ion probe, which has high transmission capability under atmospheric pressure conditions. To analyze a solid–liquid interface, the atmospheric pressure analysis system is essential, because liquid materials evaporate easily in vacuum. The volatile liquid (wet) samples, however, are difficult to measure using conventional SIMS. The mean free path of ions with energy in the keV range is very short under atmospheric pressure and these ions cannot penetrate the surface. In contrast, evaporation of liquid materials was suppressed in He at atmospheric pressure and samples containing liquid materials could be measured using the MeV-SIMS technique without dry sample preparation. Recently, we are developing a humidity controlled atmospheric pressure MeV-SIMS system, because water evaporation rate depends on the humidity strongly. In order to obtain imaging mass spectra of wet samples, it is needed to keep the wet surface of samples under ambient and humid condition for long time. In this paper, we show the results of continuous SIMS measurement of benzoic acid solution on a Si substrate in a wet He environment for solid-liquid interface analysis.
